This invention relates to color television systems.
All existing broadcast television standards have a picture aspect ratio (the ratio of picture width to picture height) of 4:3. This ratio was chosen for compatibility with ordinary motion picture standards.
A greater sense of realism could be conveyed by television pictures if the aspect ratio were increased so that the picture filled more of the viewer's field of view. Wide-screen presentations are now commonplace in cinemas. A number of proposals have been made for television standards with a higher aspect ratio, but these all involve a higher video bandwidth.
This invention enables the provision of a higher aspect ratio within the same bandwidth as existing television standards.
In the U.K. System I 625-line standard, the total length of the line is 64 .mu.s. However, only 52 .mu.s is used for the picture. This is known as the active line period. The remaining 12 .mu.s, known as the horizontal blanking interval, is required to transmit a synchronising pulse for the horizontal synchronising of the receiver, a black level pulse which provides a d.c. clamping reference, and a burst of color subcarrier to synchronise the receiver's PAL decoding circuits. The receiver uses the time of the horizontal blanking interval for horizontal flyback of the scanning spot in the cathode ray tube to the start of the next line.